The construction and operation of light control films, also known as light collimating films or visual protection foils, is well known. Light control films are used to regulate the directionality of transmitted light. For example, see WO2010/090924 and US2010/0201242. These films have a plurality of parallel grooves or light control structures, which are formed of alternating structures of light absorbing material and light transmitting material, so that depending on the orientation of the grooves, the pitch and the geometry, the films provide a maximum light transmission at a predefined angle and an image cut off or black out for angles different from the predefined angle. When the film is viewed at a first viewing angle, light is transmitted through the film allowing one to see substantially unobstructed through the film so that the film appears to be substantially transparent. However, when the film is viewed at a second viewing angle, light is blocked and the film appears dark, thereby preventing seeing through the film.
Identification documents such as identification cards, credit and debit cards, driver's licenses, and the like, and passports, are personalized with information concerning the intended holder of the identification document and then issued to the intended holder. Personalization and issuance are typically handled by government agencies, credit card companies, or other entities authorized to handle the personalization and issuance process.
As part of the personalization and issuance process, the identification documents can undergo a number of personalization procedures, including printing, portrait printing, magnetic stripe and/or chip encoding, embossing, lamination of protective laminates, and other known procedures.
A number of security measures have been implemented in order to resist counterfeiting, forgery or tampering with identification documents.
One technique uses laser engraving because of the advantage that the information can be written inside the document layers using the laser, so that the information cannot be removed, modified, or replaced from the surface like printing. With laser engraving, the document must consist of appropriate material, which reacts in the designated way to the laser.
In order to avoid copying and direct printing, one known security feature uses a lens structure on the top surface, and the laser beam transmits through the lens structure and engraves the layer underneath so that several different images can be placed at the same area visible under different angles. This approach is described in U.S. Pat. No. 4,765,656, U.S. Pat. No. 4,892,336, and WO 2006/137738. Following this approach, several images can be engraved underneath the lens structure, which join together to form one image with a three dimensional appearance, as disclosed in WO 2006/110038 and WO 2011/122943.
Another security feature as described in U.S. Pat. No. 6,786,513 is visible from both sides of the document so that a falsification by modifying the surface can easily be detected. The feature uses a laser to form micro holes with different sizes into the document. The generated perforation pattern is visible when viewed against a bright background. This feature involves the complete thickness of the document including all layers. The drilled holes perforate the surface of the document so that the document gets susceptible to soiling. In addition, conventional drilling machines with needle sized drilling bits may be able to imitate the feature.
An example of a previous security feature that is ablated into a foil is disclosed in U.S. Patent Application Publication US 2011/0037247.
Further improvements to security measures to resist counterfeiting, forgery or tampering with identification documents, as well as resist fraudulent use of identification documents once issued, are needed.